Typically in an internal combustion engine, the intake and exhaust valves are controlled mechanically. The valves are mechanically controlled by the camshaft of the engine and thus there is limited flexibility in the control of the valves. Valve control is extremely important for optimizing fuel economy and reducing emissions. Therefore, flexibility is highly desirable in valve control.
It is known in the art to employ electromagnetically driven valve actuators in an internal combustion engine. Typically, these known systems require power circuits having high frequency switching devices in order to handle the voltage differences required to properly control the valves. Additionally, the control of the valve timing is critical and therefore, is the subject of much consideration.
A typical electromagnetic valve system includes a first solenoid coil spaced apart from a second solenoid coil. An armature mechanically contacting a valve stem moves between the first armature coil and the second armature coil. A pair of springs is used to return the armature to an at rest position between the first solenoid coil and the second solenoid coil. Thus, to open the valve the lower solenoid coil electromagnetically draws the armature thereto against the spring force. To close the valve the upper solenoid is engaged to draw the armature toward the second solenoid. Known systems operate, for example, with one solenoid coil on while the other solenoid coil is off and in reverse for a reverse position of the valve.
Another known system is found in U.S. Pat. No. 5,748,433. In this system, a solenoid is provided with a current in a first direction for holding the armature in a predetermined direction. The current is then interrupted and a reverse polarity current pulse is provided to the solenoid after a predetermined time period. In this configuration the pulse applied is fixed in duration and thus cannot account for operating conditions of the vehicle, wear or manufacturing tolerances. By not compensating for these factors, the amount of energy used in the reverse polarity pulse may be greater than necessary. By waiting to apply the reverse polarity current pulse, more energy must be consumed to overcome the momentum of the valve. Therefore, the system is believed to have increased energy consumption which reduces the fuel economy of the engine.
It would therefore be desirable to reduce the power consumption of a valve operation system for an engine of an automotive vehicle to realize fuel economy.